1. Field of the Invention
The present invention relates to a method and apparatus for controlling a power supply.
2. Description of the Related Art
In general, many electronic apparatus, such as lap-top personal computers or word processors, are operated by an AC adapter and/or an incorporated chargeable battery. The battery is charged, with a current, i.e., a charge current, supplied from the AC adapter.
In the electronic apparatus of this type, the battery is generally charged with a constant current. When the battery is charged with a constant current, the battery voltage of the battery gradually increases from the start of charging. When the battery voltage approaches to the voltage corresponding to the full charge state, the battery voltage rapidly increases and when the battery voltage reaches a voltage corresponding to the full charge state, the battery voltage decreases. This is due to the characteristics of the battery, and in general used secondary batteries have such characteristics.
In a conventional electronic apparatus, the full charge state of a battery is detected on the basis of a voltage decrease occurring after the battery voltage becomes equal to the voltage corresponding to the full charge state. In other words, the conventional electronic apparatus determines that the battery is in the full charge state when the battery voltage becomes maximum. Therefore, the battery is to be overcharged.
If an overcharge occurs while the battery is charged with a large amount of current, i.e., rapid charge is being executed, the performance of the battery is affected.
A conventionally used nickel-cadmium battery is not much affected by overcharge in the performance of the battery. However, a nickel-hydrogen battery which is expected to be a main secondary battery is adversely affected by overcharge in the performance of the battery. Therefore, in the case where the battery such as the nickel-hydrogen battery is incorporated in a conventional electronic apparatus for detecting a full charge state of the battery by utilization of a decrease in the battery voltage, since overcharge is executed, the performance of the battery is adversely affected.
Under the circumstances mentioned above, there is a demand for a power source control apparatus which allows detection of the full charge state of a battery, without overcharge occurring.